Embodiments of the present invention generally relate to MRI compatible leads and more particularly to leads that exhibit low heating when exposed to MRI fields.
Numerous medical devices exist today, including but not limited to electrocardiographs (“ECGs”), electroencephalographs (“EEGs”), squid magnetometers, implantable pacemakers, implantable cardioverter-defibrillators (“ICDs”), neurostimulators, electrophysiology (“EP”) mapping and radio frequency (“RF”) ablation systems, and the like (hereafter generally “implantable medical devices” or “IMDs”. IMDs commonly employ one or more conductive leads that either receive or deliver voltage, current or other electromagnetic pulses from or to an organ or its surrounding tissue for diagnostic or therapeutic purposes. The leads include bare or insulated coiled wire forming one or more tightly wound solenoid-like structures along the shafts. These tightly wound coils facilitate torque transfer, prevent “buckling” and allow the conduction of electrical signals to and from the proximal (system) end to the distal (patient) end of the device. The lead may represent a catheter, an ICD lead, a neurostimulation lead, a pacemaker lead and the like. When exposed to electromagnetic fields, such as for example those present in magnetic resonance imaging (“MRI”) systems, these leads may sustain undesired currents and/or voltages that interact with the surrounding blood and tissue, potentially resulting in unwanted tissue heating, nerve stimulation or other negative effects resulting in erroneous diagnosis or therapy delivery.
Existing implantable medical leads for use with implantable pulse generators, such as neurostimulators, pacemakers, defibrillators or implantable cardioverter defibrillators (“ICD”), are prone to heating and induced current when placed in the strong magnetic (static, gradient and RF) fields of a magnetic resonance imaging (“MRI”) machine. The heating and induced current are the result of the lead acting like an antenna in the magnetic fields generated during a MRI. Heating and induced current in the lead may result in deterioration of stimulation thresholds or even increase the risk of cardiac tissue damage.
Over fifty percent of patients with an implantable pulse generator and implanted lead require, or can benefit from, an MRI in the diagnosis or treatment of a medical condition. MRI modality allows for flow visualization, characterization of vulnerable plaque, non-invasive angiography, assessment of ischemia and tissue perfusion, and a host of other applications. The diagnosis and treatment options enhanced by MRI are only going to grow over time. For example, MRI has been proposed as a visualization mechanism for lead implantation procedures.
A need remains for an improved MRI compatible lead that addresses the above problems and other issues that will be apparent from the following discussion and figures.